Final answer:
To find the value of 3x², substitute 2x+3 into f(x) = 2x+3 in the equation f(2x+3) = 5x. Then solve for x and substitute the value back into 3x² , and we get 60.75.
Step-by-step explanation:
To find the value of 3x², we need to substitute 2x+3 into f(x) = 2x+3 in the equation f(2x+3) = 5x. This gives us:
f(2x+3) = 5x
2(2x+3) + 3 = 5x
4x + 6 + 3 = 5x
7x + 9 = 5x
2x = -9
x = -4.5
Now we can substitute the value of x back into 3x²:
3(-4.5)² = 3(20.25)
= 60.75